Photolithographic processing is an important technology in the manufacturing of integrated circuits (ICs). Photolithography, or like lithographic techniques (i.e. X-ray lithography, E-beam exposure, phase shift technology, etc.), is usually used several times during the course of fabricating an integrated circuit wafer.
Conventionally, photolithography requires that a layer of organic photoresist be formed over the IC wafer. This photoresist or resist is typically applied by spraying an organic light-sensitive photoresist over the IC wafer while the wafer is being rotated at a predetermined number of rotations per minute (RPM). The RPM is selected to provide a photoresist layer which has a relatively planar topography and thickness.
In most cases, after photoresist is applied to an IC wafer, the IC wafer and photoresist layer are exposed to a thermal heat cycle or a like thermal step. This heat cycle, known also as a "soft bake", bakes the photoresist onto the IC wafer surface to ensure adequate photoresist adhesion and limited subsequent photoresist peeling.
A mask, usually made of chromium opaque regions and a quartz substrate, is positioned over the IC wafer. A lamp or like energy source selectively exposes portions of the photoresist layer on the IC wafer through the mask. The light exposure alters the molecular weight of exposed portions of the photoresist layer while leaving the molecular weight of unexposed portions unchanged.
A solution or chemical, known also as a "developer", is then used to "develop" or etch the photoresist. The developer etches the photoresist selectively as a function of the molecular weight. Some developers etch photoresist molecules having a low molecular weight, and other developers etch photoresist molecules having a high molecular weight. By using the developer, a masking pattern defined by the mask is transferred to the photoresist layer which overlies the IC wafer. In some cases, a "hard bake" is performed after the photoresist development step to bake the photoresist a second time.
The photoresist pattern which overlies the IC wafer is then used to etch or form patterns/regions in layers which underlie the photoresist. Once the photoresist has been used to form IC patterns in underlying layers, an etch step is used to remove all portions of the photoresist. Known ash steps, wet etch techniques, cleaning cycles, de-ionized water rinses, and/or like processes are used to clean the IC wafer after being exposed to photoresist.
Although photoresist is used extensively in IC processing, photoresist has some disadvantages. Photoresist processing, as indicated above, requires many processing steps. Also photoresist is a source of unwanted IC contaminants such as metal contaminants and sodium. Exposing photoresist to certain etch chemistries, plasma environments, and the like may create undesirable organic layers known as "veils" or "scum" which overlie an IC wafer. These undesirable organic layers are difficult to remove and may reduce yield or increase contact resistance. Other known problems with photoresist, such as reflective notching, etc., exist in the art.
Another material which may be patterned in a manner similar to photoresist is polyimide. Polyimide is an organic material and is susceptible to contamination in a manner similar to photoresist. Polyimide is also not an adequate diffusion barrier, is difficult to control in terms of film thickness, has stress-related problems, and does not have adequate sub-micron resolution capabilities.
Therefore, an improved lithographic process and lithographic material is desired.